U.S. seasonal flu kills 13,000 since Jan.

ATLANTA, April 28 (UPI) -- There have been no U.S swine flu fatalities so far, but since January more than 13,000 people have died of complications from seasonal flu, officials said.

The Centers for Disease Control and Prevention's weekly report said no fewer than 800 flu-related deaths were reported in any week between Jan. 1-April 18, the most recent week for which figures were available, CNN reported Tuesday. Seasonal flu is expected to keep killing hundreds of people every week for the rest of the year.

The researchers looked at deaths in the 122 largest U.S. cities with about 9 out of 10 of the deaths among people age 65 or older, the reports said.

Dr. Brian Currie, medical director at Montefiore Medical Center in New York, said most times the elderly already have health problems that the flu makes worse.

"Regular influenza can be taxing," Currie told CNN. "It causes their underlying disease to decompensate and then they don't have the reserves to get through it. While it may not be the direct cause listed on the death certificate, it certainly contributed."

Worldwide annual death from seasonal flu is estimated between 250,000 and 500,000, the CDC report said.

One of the reasons medical experts are concerned about swine flu is that many of the more than 150 who died in Mexico have been young and otherwise healthy.